I had heard that the days of the week came from the names of the
Titans.  This corresponds to the "planet names" idea, since that's
what the Titans were mapped to.  Look at the day names:

Sunday (Sun Day), from Latin dies solis, from Greek hemera heliou;
  see also French demanche and Spanish domingo (same root as Latin
  dominari, to master/control); German Sontag.

Monday (Moon Day), from Latin lunae dies.  See also French lundi,
  Spanish lunes.

Tuesday (Tiu's Day), not well translated from Latin dies Martis (Mars),
  French mardi, Spanish martes.  Tiu (also spelled Tew) is an "English
  god of the sky and of war; the equivalent of Tyr in Scandanavian
  mythology."  Yeah, sounds like our buddy Ares all right.

Wednesday (Woden's Day), Latin Mercurii dies (Mercury); French
  mercedi, Spanish miercoles (sp?).  Woden is the chief god in the
  Anglo-Saxon pantheon, equivalent of Odin.  This one I don't get;
  Odin is the Zeus/Jupiter god.  Looks like the Anglo-Saxons messed
  up here; maybe they had no Mercury (winged messenger) equivalent.

Thursday (Thor's Day), Latin dies Jovis (Jupiter), French jeudi,
  Spanish jueves, German Donnerstag.  Thor is the Scandanavian
  Thunder God.  But Odin is the boss god; see Wednesday.

Friday (Freya's Day), no Latin given, compare French vendredi,
  Spanish viernes (hmm, these sound more like "market day" than
  "Venus' Day").  Freya is the Teutonic goddess of love, beauty
  and fecundity (sounds a lot like Venus).

Saturday (Saturn's Day), Latin Saturni dies, French Samedi, Spanish
  Sabado (Sabbath).


Sure looks like heavenly bodies, doesn't it?  Let's here it for
the tenacity of pagans and polytheists everywhere!  Even the
oft-rewritten Bible couldn't root us out!